How to check if element exists in array with jq

I have an array and I need to check if elements exists in that array or to get that element from the array using jq, fruit.json:

{
    "fruit": [
        "apple", 
        "orange",
        "pomegranate",
        "apricot",
        "mango"
    ]
}


cat fruit.json | jq '.fruit .apple' 

does not work

The semantics of 'contains' is not straightforward at all. In general, it would be better to use 'index' to test if an array has a specific value, e.g.

.fruit | index( "orange" )

However, if the item of interest is itself an array, the general form:

 ARRAY | index( [ITEM] )

should be used, e.g.:

[1, [2], 3] | index( [[2]] )  #=> 1

IN/1

If your jq has IN/1 then a better solution is to use it:

.fruit as $f | "orange" | IN($f[])

If your jq has first/1 (as does jq 1.5), then here is a fast definition of IN/1 to use:

def IN(s): first((s == .) // empty) // false;

any(_;_)

Another efficient alternative that is sometimes more convenient is to use any/2, e.g.

any(.fruit[]; . == "orange")

or equivalently:

any(.fruit[] == "orange"; .)

To have jq return success if the array fruit contains "apple", and error otherwise:

jq -e '.fruit|any(. == "apple")' fruit.json >/dev/null

To output the element(s) found, change to

jq -e '.fruit[]|select(. == "apple")' fruit.json

If searching for a fixed string, this isn't very relevant, but it might be if the select expression might match different values, e.g. if it's a regexp.

To output only distinct values, pass the results to unique.

jq '[.fruit[]|select(match("^app"))]|unique' fruit.json

will search for all fruits starting with app, and output unique values. (Note that the original expression had to be wrapped in [] in order to be passed to unique.)

[WARNING: SEE THE COMMENTS AND ALTERNATIVE ANSWERS.]

cat fruit.json | jq '.fruit | contains(["orange"])'